The single leg stretch is a classical Pilates exercise for strengthening and toning the abdominal muscles. For increased abdominal challenge, stop the knee at 90 degrees of hip flexion instead of hugging the knee into the chest. Actively stretch through the legs, flatten the abs and keep the shoulders down with each movement and this exercise will tone many muscles in the body. Watch this how to video and you'll be getting in shape with pilates in no time.